1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to a method for controlling defrosting in a microwave oven, in which an actual temperature of a surface of food is detected continuously during defrosting of the food, for controlling a defrosting process.
2. Background of the Related Art
The microwave oven heats food in a cavity by means of an ultra high frequency wave (2450 MHz) from a magnetron. In order to make an accurate food heating control in the microwave oven, an infrared sensor is fitted on one side of the cavity, for projection to the food, to detect a surface temperature of the surface of the food, and transmission of the information to a microprocessor in the microwave oven, so that the microprocessor can determine heating and control conditions thereafter based on the detected surface temperature of the food.
Referring to FIG. 1, a related art microwave oven is provided with a turntable 11 for placing food to be cooked thereon, a magnetron 12 for generating, and supplying a microwave to the food in the cavity 10 through a waveguide, a cooling fan 13 for cooling the heated magnetron 12, an infrared sensor 14 for detecting a temperature of the food, and a control part (not shown) for controlling operation of the magnetron 12.
The operation of the foregoing microwave oven will be explained. When the user provides a cooking command to the microwave oven, the control part puts the magnetron 12 into operation. A microwave generated at the magnetron 12 is directed to the cavity 10 through the waveguide, and heats the food. The infrared sensor 14 detects a surface temperature of the food, and provides a voltage for a surface temperature of the food, which signal is passed through a series of signal processing, and provided to the control part. According to this, the control part operates the magnetron 12 to heat the food until a cooking temperature reaches to a target temperature, and the cooling fan 13 during cooking for cooling the heated magnetron 12. Positions of the infrared sensor 14 and the cooling fan 13 are not limited to the positions shown in FIG. 1, but may differ depending on types of the microwave oven; different from the positions shown in FIG. 1, the positions may be varied, such that the infrared sensor is fitted to a right side of the cavity, and the cooling fan is fitted to a top of the cavity.
A defrosting process of frozen food may differ from general food heating. A related art defrosting process of frozen food in the microwave oven will be explained, with reference to FIG. 2. FIG. 2 illustrates a graph showing time vs. a temperature variation of frozen food, wherein hatched blocks denote power turned on time periods during which a power is supplied into the cavity 10 as a heating energy. That is, the magnetron is operative in periods shown in hatched blocks to direct the microwave to the frozen food inside of the cavity 10. In a case the frozen food is to be defrosted, the microwave oven is put into operation in a state a surface temperature thereof is below zero, when the infrared sensor 14 at one side of the cavity 10 detects a variation of the surface temperature of the frozen food. In the meantime, as the surface temperature of the frozen food is at a low temperature, even though the power turned on time period is long in an initial defrosting, the power turned on time period becomes shorter, gradually. That is, because a temperature of the frozen food rises gradually as the defrosting proceeds, the power turned on time periods become the shorter as a frozen food turn over time period xe2x80x98Pxe2x80x99 approaches. At the turn over time xe2x80x98Pxe2x80x99, the user opens a door on the microwave oven, turns the frozen food over, and proceeds the defrosting, again. When the defrosting is started again in a state the frozen food is turned over, a power turned on time period of the magnetron is controlled at fixed intervals baser on a time period taken from the initial defrosting to the turn over xe2x80x98Pxe2x80x99, and a power condition until the turn over time period xe2x80x98Pxe2x80x99 is reached. That is, after the frozen food is turned over, the defrosting is carried out in a certain time period and power, taking a time period taken in a first defrosting of the frozen food (a defrosting process until the turn over) and a power condition in the time period into account. Therefore, in the second defrosting process after the frozen food is turned over, a process proceeds, in which merely the magnetron 12 is turned on/off periodically based on the time period taken in the first defrosting and the power condition in the time period.
Consequently, the related art defrosting in the microwave oven has a problem in that defrosting of frozen food is not made properly in a case frozen states differ on both sides of the frozen food to be defrosted due to shape or other. In the related art defrosting, the defrosting after the frozen food is turned over is carried out regardless of the surface temperature of the turned over frozen food, that causes problems of a product reliability deterioration coming from pre-mature defrosting, or excessive defrosting, or inconvenience to the user.
Accordingly, the present invention is directed to a method for controlling defrosting in a microwave oven that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method for controlling defrosting in a microwave oven, which can control a second defrosting according to an actual temperature of frozen food.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method for controlling defrosting in a microwave oven having an infrared sensor, includes the steps of (a) controlling a first defrosting up to a preset temperature upon reception of defrosting key application from a user, (b) turning over frozen food upon completion of the first defrosting, and (c) periodically detecting a surface temperature of the turned over frozen food by using the infrared sensor, and controlling a second defrosting according to the detected surface temperature and temperature variation.
An initial voltage application time period in the step (a) or (c) is made relatively longer than the voltage application time period in a later half of each of the steps.
The step (a) includes the steps of calculating a turning over time point by using the presently progressive minimum temperature Min_T and a minimum temperature variation xcex94T, calculating a first defrosting voltage by using a greater value xcex94Tmax of the minimum temperature variation xcex94T and a maximum temperature variation xcex94Tm, and the presently progressive minimum temperature Min_T, and carrying out defrosting according to the calculation, and generating a signal sound if the minimum temperature Min_T or a maximum temperature Max_T is higher than a preset temperature, or if the turning over time point is over a preset time point.
The step (c) includes the steps of calculating a defrosting finish time point and a second defrosting time period upon reception of a starting key again after the frozen food is turned over, calculating a second defrosting voltage by using a smaller temperature variation value xcex94Tmin, and the presently progressive minimum temperature Min_T upon calculation of the defrosting finish time point and the second defrosting time period, the smaller temperature variation value xcex94Tmin being selected from the minimum temperature variation xcex94T and a maximum temperature variation xcex94Tm obtained based on the surface temperature detection of the frozen food, and finishing defrosting if the minimum temperature Min_T or the maximum temperature Max_T is higher than a preset temperature, the present time point is the same with the calculated finish time point, or the calculated defrosting time period is passed.
The voltage application condition control according to the periodic detection of a surface temperature of frozen food by an infrared sensor, not only in the first defrosting when one side of the frozen food is heated, but also in the second defrosting after the turn over of the frozen food permits an optimal defrosting of the frozen food. That is, the defrosting control based on the surface temperature and the temperature variation of the frozen food permits to prevent a pre-mature, or excessive defrosting, and the optimal defrosting made available by the present invention provides a satisfaction and reliability on the product to the user.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.